Lateral Response of Rock Socketed Single Pile Due to the Effect of Overlying Sand Layer-Paper

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The study uses three-dimensional finite-element analyses in PLAXIS 3D to assess how an overlying loose-sand layer affects the lateral response of a single pile socketed into moderately weathered, weak rock. A 600 mm concrete pile was modelled as elastic, the sand using a hardening-soil model, and the rock using the Hoek–Brown model. The researchers varied rock socket length from zero to four pile diameters and examined soil embedment-to-relative-stiffness ratios (Ls/T) from 0.75 to 3.<br /><br />Increasing socket length generally reduced pile displacement and increased lateral capacity. However, the benefit depended strongly on the thickness of the sand layer. For Ls/T values of 0.75–1.5, effective socket lengths were approximately 1.5–2 pile diameters. At Ls/T values of 2.25–3, the useful length fell to roughly 0–1 diameter; at Ls/T = 3, socketing had little or no effect. Across the cases studied, gains in bending-moment response and lateral resistance became negligible beyond about two pile diameters. A thicker sand layer increased pile displacement and shifted the depth of fixity upward, while the maximum bending moment generally increased with socket length up to a ratio of about 2.<br /><br />The results indicate that a standard, lengthy rock socket is not always necessary: the required socket length depends on the sand-layer depth relative to pile stiffness, and a short socket may provide adequate lateral resistance. These findings are based on a specific numerical model and set of soil, rock, and pile properties; the authors recommend further verification across different ground profiles and pile diameters before generalizing the conclusions.

Keywords

PLAXIS 3D

finite element analysis

lateral pile response

rock socket length

loose sand layer

single pile

Hoek-Brown model

hardening-soil model

pile displacement

lateral capacity